Aliphatic Hyperbranched Polyesters Research Articles

Rheological and physical properties of aliphatic hyperbranched polyesters

AbstractThe effects of the size (pseudo‐generation number) and nature of end groups on physical and rheological properties were investigated for a series of hyperbranched polyesters based on an ethoxylated pentaerythritol core and 2,2‐bis‐(hydroxymethyl)propionic acid repeat units. The observed linear dependence of the melt viscosity on the molar mass in the high pseudo‐generation‐number limit indicated that entanglement effects were substantially absent. Moreover, the marked influence of end capping of the end groups on the physical and rheological properties suggested that intermolecular interactions were dominated by contacts between the outer shells of the molecules, in which the end groups were assumed to be concentrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1218–1225, 2004

Facile synthesis of aliphatic hyperbranched polyesters based on diethyl malonate and their irreversible molecular encapsulation.

Synthesis of diethyl malonate based wholly aliphatic hyperbranched polyesters having suitable polar matrix for irreversible molecular encapsulation is carried out for the first time.

Rheological characteristics of hyperbranched polyesters

When the effects of physical aging below Tg are erased, the rheological response of a series of aliphatic hyperbranched polyesters is Newtonian and the melt viscosity scales roughly linearly with Mw at high Mw, indicating entanglement to be absent. The rheological behavior is also highly sensitive to the nature of the terminal groups, suggesting the overall behavior to be close to that of an assembly of compact coreshell "particles". There are therefore strong parallels between the physical behavior of the hyperbranched polyesters in question and that of their ideal dendrimer analogues.

Thermal stability of aliphatic hyperbranched polyesters

The influence of the molar mass (generation), number and type of end groups on the thermal stability of aliphatic hyperbranched polyesters are presented in this study. Different end groups were obtained by modification of the samples with chlorides of propionic acid and stearic acid. The thermal stability of the hyperbranched polyesters was determined by thermogravimetry using a NET-ZSCH TG 209 instrument in nitrogen atmosphere at a heating rate of 10?C/min. A comparison of the temperatures obtained for mass losses of 5 20 and 40 wt% for unmodified samples showed that the thermal stability increased up to the fourth generation and then remained practically constant. An increase in the thermal stability of modified samples of the second, third and fourth generation was observed.

Hyperbranched polyesters and their application in dental composites: monomers for low shrinking composites

AbstractUsing trimethylolpropane (TMP) and 2,2‐bishydroxymethylpropionic acid (Bis‐MPA), aliphatic hyperbranched polyesters (HBP) were synthesized, with a degree of branching of DB = 0.47 and a degree of polymerization of Pn = 16.5. Aromatic HBPs with repetitive units of 2,2‐bis(4‐hydroxyphenyl)pivalonic acid (Bis‐PVA) lead to a higher DB = 0.48 and Pn = 30.5 compared to the aliphatic HBP. Reactive functionalization of the hyperbranched polymers was achieved via esterification of mixtures of methacrylic acid and carboxylic acids. In this manner, i‐butyric acid and methacryloyl terminated HBPs were obtained. They have a low viscosity ranging from 200 to 364 Pa*s and exhibit relatively low volume shrinkage (1.9 to 3.6%) during photoinitiated cure. Dental composites with volume shrinkage of 0.5 to 1.5% have been prepared using these methacryloyl terminated HBPs in combination with a Ba/alumosilicate glass filler. Copyright © 2001 John Wiley & Sons, Ltd.

Melt rheology of aliphatic hyperbranched polyesters with various molecular weights

Rheological behaviour of a series of aliphatic hyperbranched polyesters, Boltorn polymers, with different molecular weights (generations) is studied in the molten state. The onset of a nonlinear region occurs at much lower strains for Boltorn polymers of lower generations (generation 2 and 3) compared with those of higher generations (generation 4 and 5) in the dynamic strain sweep experiments. Relaxation times calculated from dynamic rheological parameters using an empirical equation indicate that the generation 2 and 3 polymers relax much slower than their higher generation counterparts. The generation 2 and 3 polymers show shear-thinning behaviour, whilst higher generation materials are Newtonian, in both oscillatory and steady shears within the deformation rates investigated. The Cox–Merz rule is found to not be obeyed by all the polymers studied. With increasing temperature, steady shear viscosity of the Boltorn polymers decreases but the features of shear rate dependence, shear thinning or Newtonian behaviour, remain the same. Flow activation energies obtained from the temperature dependence of steady shear viscosity show that Boltorn polymers have higher activation energies than most linear polymers, indicating a stronger temperature dependence of flow. The generation 2 and 3 polymers exhibit greater flow activation energies than the generation 4 and 5 materials due to stronger polar interactions.

Free radical “grafting from” hyperbranched polyesters based on polymeric azo initiators

AbstractAromatic and aliphatic hyperbranched polyesters were prepared by AB2 polycondensation process. The highly branched, functional structure of these polymers leads to excellent solubility in combination with low solution viscosities. Varied numbers of the functional groups of the hyperbranched structures were modified with azo functions which are able to initiate free radical polymerization. An increase in temperature in the presence of the vinyl monomers methyl methacrylate (MMA), butyl methacrylate (BMA), styrene (S), or acrylamide (AA) results in “grafting from” the hyperbranched structure. Using this method several graft products were synthesized with variations in structure, number, and size of the graft arms. Gel‐permeation chromatography (GPC) with universal calibration and viscosity measurements indicate a strong influence of the hyperbranched core on the properties of the graft product. It was possible to control the phase behavior of the graft products from two phases to homogeneous by the ratio hyperbranched polyester: grafted monomer. The film forming properties which are very poor for unmodified hyperbranched polyester were improved by grafting with linear polymer chains.